The art of inkjet printing is relatively well known. In general, an image is produced by emitting ink drops from an inkjet printhead at precise moments such that they impact a print medium, such as a sheet of paper, at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium and emit ink drops at such times pursuant to commands of a microprocessor or other controller. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.
A conventional thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a nozzle or orifice plate attached to the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heaters fabricated by deposition, masking and etching techniques on a substrate such as silicon.
To print or emit a single drop of ink, an individual heater is uniquely addressed with a small amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local ink chamber (between the heater and nozzle plate) and be ejected through and projected by the nozzle plate towards the print medium.
During manufacturing of the printheads, a printhead body gets stuffed with a back pressure device, such as a foam insert, and saturated with mono or color ink. A lid adheres or welds to the body via ultrasonic vibration. Ultrasonic welding, however, sometimes cracks the heater chip, introduces and entrains air bubbles in the ink and compromises overall printhead integrity. Adhesion has problems because of its impractically long cure time.
Even further, as demands for higher resolution and increased printing speed continue, heater chips are often engineered with more complex and denser heater configurations which raises printhead costs. Thus, as printheads evolve a need exists to control overall costs, despite increasing heater chip costs, and to reliably and consistently manufacture a printhead without causing cracking of the ever valuable heater chip.
Regarding the art of laser welding, it too is relatively well known. In general, with reference to FIG. 1, first and second work pieces, embodied as an upper work piece 100 laid on a lower work piece 120 along a weld interface 180, become welded to one another by way of an irradiated beam 140 of laser light. As is known, the beam 140 passes through the upper work piece, which is transparent to laser light, where it gets absorbed by the lower work piece, which is laser light absorbent. As the beam irradiates, the weld interface heats up and causes the bottom surface of the upper work piece and the upper surface of the lower work piece to melt and meld together. Upon cooling, a weld joint exists. An optical path between a laser light source (not shown) and the to-be-welded work pieces may include a lens 160, for proper focusing, or other optical elements, such as mirrors, fiber optic strands, scanning structures or other. A clamping device (not shown) typically provides a pressing engagement of the work pieces to maintain relative positioning and good surface contact during welding. The beam of laser light may advance relative to the parts, such as in contour welding, or may irradiate the substantial entirety of the weld interface at substantially the same time in a simultaneous welding operation.
As is apparent in FIG. 1, the upper work piece 100 comprises a generally homogeneous material that allows laser light to transit the work piece in area A at a substantially equivalent rate as compared to area B or any other area of the work piece. Yet, when welding a lid (upper work piece) and body (lower work piece) of a container together, for example, sometimes a need exists to decorate, adorn, color code and/or emboss the lid and/or to hide the contents of the container from a user by making the lid opaque to visible light or other. In such instances, the lid may comprise constituents that make laser welding impractical, difficult or substantially impossible.
In the specific instance of making the lid opaque, perhaps to maintain the contents of a container secret, one presently known solution to the above includes the addition of an organic pigment to produce a homogeneous-composition lid that has laser light transparency characteristics and visible light opacity characteristics. As a result, a manufacturer can perform laser welding while still preventing a user from viewing the contents of the container. Such pigments, however, are exceptionally expensive and have limited chemical compatibility with some embodiments of lids.
Moreover, when an economic or other need exists to make at least the lid a plastic material, the above pigment solution often requires additional manufacturing steps such as painting or coating of the plastic to achieve the necessary opacity.
Accordingly, a need exists in the laser welding arts for economically and efficaciously laser welding two work pieces when one of the work pieces simultaneously requires laser light transparency characteristics and laser or visible light opacity characteristics.